1. Field of the Invention
The present invention relates in a first aspect to a system for assembly and maintenance of connection modules in high-voltage switchgear. From a second aspect the invention relates to a method for assembly and maintenance of such connection modules. From a third aspect the invention relates to a central component in such a system, namely a service vehicle.
2. Discussion of the Background
Such switchgear generally includes a large quantity of electrical apparatus, in the following termed connection modules, which are arranged in a number of lines, normally three, which lines are oriented in the same direction as the overhead power transmission lines entering and leaving the switchgear. Each connection module is normally supported individually on a stand, i.e. each breaker, each disconnector, each grounding device, each surge diverter and each current meter has its own stand. The large number of components required in an air-insulated high-voltage switchgear station, and the demand for safe electrical distance between each unit require that a conventional switchgear occupies a considerable ground area. The extension in the direction of the overhead power lines of a switchgear for a voltage level of 245-500 kV, defining the length of the switchgear station, is approximately 100-150 meter. A 420 kV switchgear station would be typically about 120 m.
Alternatively a plurality of electrical components may be combined in an apparatus part arranged on a common stand. Such connection modules can reduce the area occupied by the switchgear. A switchgear of such a type is described in Swedish patent application No. 96 02336-1 and various examples are described therein of how connection modules can be designed, where a common stand carries several components. The stands are placed at erection sites with base plates to anchor the stands.
When connection modules for a switchgear are to be assembled in a conventional manner the apparatus parts are transported to the respective erection sites, after which the parts are assembled on site by means of a mobile crane, for instance. Only when the apparatus parts are in place and have been assembled can the control cabling be installed and connected, usually directly to terminal blocks in the control devices.
Maintenance work such as inspection of contacts or repairs according to conventional technology is also performed on the erection site using mobile cranes or the like. Parts of the switchgear in the vicinity must be taken out of operation and rendered dead throughout the time needed for the work. Such shut-downs can entail considerable costs and it would therefore be desirable to be able to reduce or eliminate shut-downs caused by such maintenance work.
In the light of this, the object of the present invention is to provide a system for assembly and maintenance of connection modules in high-voltage switchgear in which the problems of forced shut-downs associated with conventional technology in the area are solved.
The system and method are thus based on all that work in connection with assembly and service being performed at a place other than within the switchgear area, and that the assembled or repaired connection module is transported out to its erection site. This means that such work is eliminated on site and no shut-down in operation need occur.
Transport of the connection modules could in fact be performed using a conventional fork lift truck. However, the transport places rather special demands on the transport vehicle when it is to drive a connection module out to its site, with respect to stability, anchoring of the load and accessibility in the limited space and under the special circumstances prevailing. It is therefore important that one component in the system consists of the special service vehicle defined in the claim. Such a custom-built service vehicle enables connection modules to be transported in an optimal and effective manner.
According to a preferred embodiment of the system according to the invention the service bay is situated indoors, which offers additional advantages since the work can then be performed protected from wind and weather as well as facilitating the installation of fixed aids such as overhead cranes and the like.
In another preferred embodiment the service bay is equipped with such aids and other service equipment, enabling the work to be performed effectively. The service bay according to this embodiment also includes a stock of spare parts and/or complete connection modules in reserve. When a connection module is to be repaired or serviced it can merely be transported out of the way and replaced by a similar module ready for use from stock.
According to a further preferred embodiment of the system, a number of grounding points are arranged within the area of the switchgear, and the service vehicle can be connected optionally to any of these grounding points. During transport of a connection module in upright position, therefore, its stand part will be grounded while its apparatus part is separated from ground by the insulators. It can therefore be transported close to live modules, and even touch these, without risk of electric flashover.
According to a preferred embodiment the service vehicle has a frame which is open in one direction so that it can straddle the stand of a connection module, thereby enabling fast and simple loading of the module and stable transport.
In a preferred variant of this embodiment the opening can be closed so that, when the stand of the module has been straddled, the vehicle has a closed frame thereby increasing its stability considerably.
According to another preferred embodiment the service vehicle is provided with support members, vertically movable in relation to the frame, to facilitate lifting the connection module from its base plate when it is to be transported. The support member suitably comprises a pair of beams that are raised and lowered together.
It is advantageous for the service vehicle to be designed with, on the one hand, a broad wheel base but, on the other hand, a narrow waist part. Stability during transport is then achieved, as well as flexibility to move between the modules in the switchgear station. To further increase its ability to turn around between the modules it is advantageous if the wheels can be steered individually.